Alternate power systems for use during utility power failures such as outages (blackouts) or low voltage situations (brownouts) are becoming increasingly common. In the event of utility power failures, such systems provide an alternate source of AC voltage for important electrical loads, such as emergency lighting, computers, or safety devices, thereby allowing such loads to operate or continue to operate for hours at a time. Such operation or continued operation can provide important safety benefits. In a commercial establishment, for example, operation of emergency lighting loads allows customers and employees to exit the establishment with enhanced visibility during a utility power failure.
Indeed, alternate power systems have proven so beneficial that they are often required in many different types of facilities including schools, hospitals, water treatment plants, prisons, commercial establishments and industrial plants. These same requirements also demand regularly recorded maintenance and testing of such systems to ensure their operability when utility power failures ultimately occur.
Various systems and methods are known to provide alternate power in the event of utility power failures. Among the most common are internal combustion engine driven generators. Such generators, however, can suffer from space requirement, noise, ventilation and maintenance problems. Moreover, the regularly recorded testing of such generator systems and methods can be expensive and troublesome as it must be performed manually.
Most importantly, however, such generator systems and methods for providing alternate power in the event of utility power failure are incapable of adjusting to the type of electrical load present. More specifically, when utility power is restored, emergency lighting loads must be deactivated and primary lighting loads must be reactivated. Where such primary lighting loads are incandescent or fluorescent in nature, such reactivation may be undertaken immediately.
However, where such primary lighting loads are High Intensity Discharge (HID) in nature, such as Metal Halide or High Pressure Sodium (HPS), reactivation may not be undertaken unless and until sufficient time has elapsed since the start of the utility power failure for the primary lighting loads to have properly cooled. In such cases, reactivation may have to be delayed for as long as 20-30 minutes, depending on how long the utility power failure lasted.
The generator systems and methods described above attempt to overcome this problem by assuming that all utility power failures are momentary, and delaying reactivation for a period of time equal to the "cool down" period of the primary lighting load present. However, since reactivation actually need only be delayed for a period of time equal to the cool down period of the primary lighting load minus the duration of the utility power failure, this is only a partial solution. Indeed, in many situations, such systems and methods remain active for longer than is necessary, wasting fuel and shortening generator life.
Solid state sinewave inverter systems and methods are also commonly utilized to provide alternate power in the event of utility power failures. This is especially true where computer equipment and energy efficient lighting type loads are commonly found. Such systems and methods solve many of the space requirement, noise and maintenance problems associated with the aforementioned generator systems and methods.
Solid state inverter systems and methods operate on the principle of electronically inverting a DC input voltage (from a DC power source such as a battery) to produce an AC output voltage. A number of different types of solid state inverters may be used in such systems and methods, including square wave inverters, ferroresonant inverters, and Pulse-Width Modulated (PWM) inverters.
Such inverter systems and methods, however, still suffer from a variety of problems. First, as with generators, the regular testing required for such systems and methods must still be conducted and recorded manually. Moreover, as with generators, such inverter systems and methods also suffer from the HID lighting load reactivation problem. Indeed, this problem is worse with such inverter systems and methods than with generators. Not only is the battery power wasted and batter life shortened, the battery recharging time is lengthened as well.
Consequently, a need has developed for a solid state inverter system and method for providing alternate power to an electrical load in the event of utility power failure that overcomes the reactivation problem associated with HID primary lighting loads. Such a system and method would also be microprocessor controlled to automate required testing and recordation of results, as well as to provide various instantaneous output messages for improved operation and maintenance.